Chemical vapor deposition apparatus for manufacturing semiconductor devices, its driving method and method of optimizing recipe of cleaning process for process chamber

ABSTRACT

There is provided a method of optimizing recipe of in-situ cleaning process for process chamber after a specific process on semiconductor wafers by using Residual Gas Analyzer Quadrupole Mass Spectrometer (RGA-QMS). According to the present invention, a Chemical Vapor Deposition (CVD) apparatus for manufacturing semiconductor devices comprises: a process chamber; process gas supply line for supplying process gas into the process chamber; a waste-gas exhaust line for removing the waste-gas from the process chamber after process; a supply line for supplying a CIF 3  gas into the process chamber; a sampling manifold for sampling the gas inside process chamber by using pressure difference; and RGA-QMS for analyzing the sampling gas, and the optimization of the end points according to gas flow, pressure, and temperature of the cleaning process for the process chamber is achieved through the analysis by above RGA-QMS.

[0001] This application is a divisional of U.S. Pat. No. 09/183,599,filed on Oct. 29, 1998, now pending.

FIELD OF THE INVENTION

[0002] The present invention relates to a Chemical Vapor Depositionapparatus for manufacturing semiconductor devices, its driving method,and a method of optimizing a cleaning process for the process chamber.More particularly, the invention relates to in-situ cleaning of processchamber after processing of semiconductor wafers by using Residual GasAnalyzer Quadrupole Mass Spectrometer (RGA-QMA).

DESCRIPTION OF THE RELATED ART

[0003] Generally, the semiconductor device fabrication process iscarried out inside a process chamber having certain pre-set processconditions. In particular, when a CVD (Chemical Vapor Deposition)process is performed on a semiconductor wafer, a layer of material isdeposited not only on the wafer, but also on the inner wall of theprocess chamber tube, and the boat(s) for moving the wafers between theprocess chamber and a loadlock chamber where the wafers are stored. Asthese unwanted layers are repeatedly stressed during theloading/unloading of the wafers, particles are released into the chamberthat can cause defects on the wafer during the fabrication process.

[0004] In order to reduce the causes for defects, PM (PreventiveMaintenance) is repeatedly conducted to clean the process tube atregular intervals, but the productivity of semiconductor devices isdecreased due to the interruption of the process line operation.

[0005]FIG. 1 illustrates a conventional PM sequence for a generalprocess tube. First, the system is cooled down after carrying out aspecific process on semiconductor wafers. After the process chamber iscompletely cooled, the tubes of the process chamber are taken out one byone so as to carry out wet-etch cleaning of the tubes. The wet-etchgenerally uses chemicals such as HF group in order to remove polysiliconfilm or siliconnitride film from the inside of the process tube. Then,the removed tubes are assembled inside the process chamber and a vacuumtest is performed. Process Recertification is carried out to see if theprocess chamber is ready for a new process and if the process conditionsfor the next process are substantially set up therein.

[0006] However, the above PM process represents considerable efforts andexpenses, and takes over 24 hours to complete. Therefore, in order toovercome the problems, a plasma etch of using NF₃ and CF₄ gas is carriedout instead of the wet-etch. Alternatively, Thermal Shock Technology isused for removing the layers formed by thermal stress inside thechamber, or the chamber is dry-etch using CIF₃, BrF₅.

[0007] However, even though these technologies are employed, the tubesstill must be removed and reassembled and the expense, the labor, anddowntime remain as problems.

SUMMARY OF THE INVENTION

[0008] The present invention is directed to provide a CVD apparatus formanufacturing semiconductor devices wherein a process chamber isequipped with cleaning gas supply line, a sampling manifold, and a gasanalyzer which are used to clean the tubes in situ. As a result, themethod of the present invention substantially obviates one or moreproblems, disadvantages, and limitations of prior art.

[0009] Another object of the present invention is to provide a method ofdriving the CVD apparatus, wherein a specific process is performed onwafers, and then in-situ cleaning is performed inside a process chamber,after semiconductor wafers are unloaded.

[0010] Another object of the present invention is to provide a method ofoptimizing a cleaning process for a process chamber.

[0011] To achieve these and other advantages and in accordance with thepurpose of the present invention as embodied and broadly described, aCVD apparatus of the present invention includes a process chamber inwhich a deposition process for manufacturing semiconductor devices iscarried out; a plurality of process gas supply lines for supplyingprocess gases to the process chamber; a waste-gas exhaust line forremoving the waste-gas from the process chamber; a cleaning-gas supplyline for supplying a cleaning gas to the process chamber; a samplingmanifold connected to the process chamber for sampling the gas insidetherein by using pressure difference; and a gas analyzer for analyzingthe sampling gas from the sampling manifold.

[0012] Preferably, the process chamber is a Low Pressure Chemical VaporDeposition (LPCVD) chamber having a sealed outer tube and an inner tubehaving an open top inside the outer tube. The cleaning gas is ClF₃. Thecleaning-gas supply line is connected to the inner tube, and thesampling manifold is connected to the outer tube. An orifice isinstalled in the sampling manifold such that the pressure therein ismaintained at the same pressure as in the process chamber. The samplingmanifold comprises a first air valve, a second air valve, a firstisolation valve, a second isolation valve, a third isolation valve, anda gate valve between the connecting point with the outer tube. Apurge-gas supply line is also provided in the sampling manifold. Thepurge-gas supply line of the sampling manifold is connected to the firstair valve and the second air valve respectively from the purge gassupply source, and third and a forth air valves are further providedbetween them respectively. A Capacitance Manometer (CM) gauge and asampling pump are preferably installed between the first isolation valveand the second isolation valve of the sampling manifold in order tocontrol the first pressure of the sampling manifold.

[0013] A scrubber is provided for receiving and cleaning the waste-gaspassing through the waste-gas exhaust line, and the gas sampling line.

[0014] The gas analyzer is preferably a RGA-QMS(Residual GasAnalyzer-Quadrupole Mass Spectrometer) comprising a mass-analyzer, aturbo pump, and a baking pump, which is preferable in the aspect ofenvironmental protection.

[0015] The invention is also embodied in a method of driving a CVDapparatus for manufacturing semiconductor devices. The CVD apparatusincludes: a process chamber; a plurality of process gas supply lines forsupplying process gases into the process chamber; a waste-gas exhaustline for removing the waste-gas from the process chamber afterprocessing; a cleaning-gas supply line for supplying a cleaning gas tothe process chamber; a sampling manifold connected to the processchamber; and a gas analyzer for analyzing the sampling gas from thesampling manifold. The method comprises the steps a) sampling the gasfrom the process chamber; b) outgasing while baking the gas in order toreduce the initial background of the gas analyzer below a certain value;c) conducting a contamination analysis of each of the process gas supplylines; d) performing a specific process for the semiconductor waferscontained in the process chamber) unloading the wafers after the abovespecific process is completed, and exhausting the waste-gas from theprocess chamber; and f) cleaning the inside of the process chamber bysupplying a cleaning gas thereinto.

[0016] The sampling manifold and the gas analyzer are continuouslypurged with a purge gas before conducting the sampling to ensure theprecision of the gas analyzer. The contamination analysis for theprocess gas supply line is performed by passing nitrogen gas througheach isolated process gas supply line and checking for leakage.Preferably, the fabrication process of semiconductor wafers is the onefor forming a silicon-containing layer on the wafer, and the cleaningprocess is conducted by introducing nitrogen gas and ClF₃ gas ascleaning gases while maintaining uniform pressure and inside the processchamber so that the end point of the cleaning process is easilydetected.

[0017] The method further comprises a step of measuring particles insidethe process chamber before and after the cleaning process, and the stepof measuring metal/ion contaminants inside the process chamber beforeand after the cleaning process so as to determine the effectiveness ofthe cleaning process.

[0018] To achieve still another object of the present invention, amethod of optimizing the cleaning process for a process chamber, thecleaning process carried out in-situ after a specific process isperformed for a wafer placed inside the process chamber, with a cleaninggas supply line for supplying the cleaning gas into the process chamber,a sampling manifold connected to the process chamber, and a gas analyzerfor analyzing the sampling gas from the sampling manifold. The methodcomprises: a) after performing a specific process on the semiconductorwafer, cleaning the process chamber by supplying a certain amount ofnitrogen gas and ClF₃ as cleaning gas while maintaining a constantpressure and temperature inside the process chamber until the cleaningend point by the gas analyzer ; and b) after performing the samespecific process for another semiconductor wafer, cleaning the processchamber by supplying a certain amount of nitrogen gas and ClF₃ ascleaning gas, and varying the pressure and the temperature inside theprocessing chamber until the cleaning end point by the gas analyzer.

[0019] Preferably, the end point of the gas analyzer is determined bythe intersecting point of amplified traces for an etch gas and theetching byproducts.

[0020] According to the present invention, when a specific process isperformed on a semiconductor wafer and the cleaning process is carriedout inside the process chamber by using ClF₃ gas, the mechanism isexactly monitored, and the composition of the cleaning process isoptimized to simplify the process and to improve process efficiency.

[0021] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory and are intended to provide further explanation of theinvention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In the accompanying drawings:

[0023]FIG. 1 is a brief representation showing the conventional sequenceof a cleaning process for the process tube of the conventional ChemicalVapor Deposition (CVD) apparatus for manufacturing semiconductordevices;

[0024]FIG. 2 is a schematic representation showing the CVD apparatus formanufacturing semiconductor devices according to one embodiment of thepresent invention;

[0025]FIG. 3 shows a sequence for the process analysis and the cleaningprocess in the CVD apparatus of FIG. 2 according to one embodiment ofthe present invention;

[0026]FIG. 4 shows an analysis trend for the storage polysilicondeposition process according to one embodiment of the present invention;

[0027]FIG. 5 shows an analysis trend for the cleaning process accordingto one embodiment of the present invention;

[0028]FIG. 6 is a graph correlating etch rate in the cleaning process topressure inside a process chamber according to one embodiment of thepresent invention;

[0029]FIG. 7 is a graph correlating etch rate in the cleaning process totemperature inside a process chamber according to one embodiment of thepresent invention; and

[0030]FIG. 8 is a graph correlating etch rate in the cleaning process toClF₃ flow inside a process chamber according to one embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Reference will now be made in detail to the preferred embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings.

[0032]FIG. 2 is a schematic representation showing the CVD apparatus formanufacturing semiconductor devices according to one embodiment of thepresent invention. A process chamber 10 comprises an outer tube 14 andan inner tube 16. Inside the process chamber 10, various processes suchas deposition process, plasma process, diffusion process, or CVDprocess, etc. are performed. A loadlock chamber 12 is installed belowthe process chamber. A boat 18 for holding wafers to be processed ismoved up and down between the process chamber 10 and the loadlockchamber 12 by an elevator 20. A gas supply line 22 for supplying processgas for processing is connected to the lower side of the inner tube 16.The gas supply line 22 may have a separate pipe line and valve for eachprocess gas or cleaning gas. In the system shown in FIG. 2, individualprocess gas supply lines and valves 32,34,36,38,40 are provided for SiH₄supply source 24, PH₃ supply source 26, N₂ supply source 28, and ClF₃supply source 30 respectively. The ClF₃ supply source 30 is a cleaninggas supply source, which will be mentioned below. The gas supply line 22may have a separate pipe line for each process gas or cleaning gas.

[0033] Meanwhile, the process waste-gas is evacuated from otter tube 14,through a discharge line 42, by a discharge pump 44, and is then routedto scrubber 46 for cleaning.

[0034] In order to, monitor the gas composition inside the processchamber 10, a sampling port 48 is installed in the outer tube 14, Thesampling port 48 is connected to a sampling manifold 50, preferably byusing a flexible connecting line 52. Sampling line 54 of samplingmanifold 50 is made of ⅓ inch diameter electropolished stainless steelpipe. Flow through sampling line 54 is controlled by a first air valve62, a second air valve 66, a first isolation valve 68, a secondisolation valve 70, a third isolation valve 72, and a gate valve 74. Thefirst isolation valve 68 and the second isolation valve 70 are eachfitted with a 100 micron orifice; and the third isolation valve 72 isfitted with a 250 micron orifice.

[0035] The sampling manifold 50 has an N₂supply source 56 for use as apurge gas, which is available whether or not samples are being drawn.The vacuum system can be damaged by the concentration of the gas due toa small amount of water inside the Gas Distribution System (GDS) so thatit is very important to precisely control the purge cycle or cleaningtime for the process chamber. The N₂ 58 is connected to the first airvalve 62 and to the second air valve 66. Further, a CM gauge 76 isinstalled between the first isolation valve 68 and the second isolationvalve 70 on sampling line 54. Sample line line 54 is connected tosampling pump 90, which discharges to the scrubber 46.

[0036] Meanwhile, sampling line 54 is connected to a gas analyzer 80through gate valve 74. The gas analyzer 80 uses a commercially availableRGA-QMS (Residual Gas Analyzer-Quadrupole Mass Spectrometer 84. An iongauge 82 is installed on the mass analyzer 84. Sample gases pass througha turbo pump 86 and a baking pump 88, and to the scrubber 46

[0037] Meanwhile, the ClF₃ gas for use in the present invention is acleaning gas that can be also used in the cleaning of polysilicon,siliconnitride, silicon glass, and tungsten silicide. It can be used inthe low temperature state as well as plasma state, and has the excellentchemical selectivity so that it performs etching at the portions whereplasma cannot reach. It also has the advantage that it is highlyunlikely to generate particles that could contaminate the wafer surface.In use ClF₃ is generally diluted to a concentration of 20±5 volume %with an inert gas such as N₂. While the lower pressure in the processchamber is good for the uniform etch for the layer inside the chamber,the higher mixing rate of etch gas is good for increasing the etch rate.It is preferable to heat the process chamber to a temperature higherthan the boiling point of the ClF₃, prior to the introduction of ClF₃and preferably higher than 400° C. for the desirable etch rate. SinceClF₃ is a very reactive gas, if the etch rate is too high, tubes 14 and16 could also be etched, shortening the useful life of the tube.

[0038] The ClF₃ supply pipe is preferably formed of nickel, monel,hastelloy, 316L stainless steel, or a polymeric material due to theproperties of the ClF₃.

[0039] Meanwhile, the RGA-QMS (Residual Gas Analyzer-Quadrupole MassSpectrometer) used as the gas analyzer 80 is operated in such a mannerthat sampled gas from the process chamber is ionized by bombardment withelectrons accelerated with 70 eV. Then, Quadrupole Mass Spectrometerpasses only those ions having a specific rate of mass to electriccharges so as to obtain a mass spectrum. By the composition of the ionsachieved from the above results, the composition of the sampled gas canbe determined. The RGA-QMS used in the present invention is a portablesystem, and unlike general OIS (Open Ion Source) used in the sputteringprocess, the ion source is a CIS (Closed Ion Source) so that it ispossible to analyze the process gas as well as bulk gas.

[0040] The sampling pressure is controlled uniformly below the processchamber pressure by the orifices (100/250 micron) inside the samplingmanifold 50.

[0041] Turning now to FIG. 3, a sequence for the process analysis andthe cleaning process in the CVD apparatus of FIG. 2 will now bedescribed. First, gas analyzer 80 is connected to the sampling manifold.N₂ gas is continuously supplied to purge the RGA-QMS. First air valve 62and third air valve 60 are closed; second air valve 66 and fourth airvalve 64 are opened. Then, fourth air valve 64 is closed, and first airvalve 62 is open, and the gas inside the process chamber 10 is sampled.At this stage, if it is necessary to control the pressure both in theprocess chamber 10 and the sampling line 54, it can be done by operatinga sampling pump 90 based on the pressure indicated on a CM gauge 76.

[0042] Then, the RGA-QMS baking evaluation is conducted. That is, afterplacing a quadrupole mass spectrometer inside an RGA-QMS chamber (notshown), baking is carried out in order to decrease the background. SinceRGA-QMS is very sensitive to contamination, its contamination level isdetermined by analyzing the background spectrum as part of every test tomeasure contamination if any, by water and oxygen. When thecontamination level is high, the RGA-QMS chamber is baked at about 250°C., and the sampling manifold is baked at about 150° C. so as to reducethe contamination level. During baking, the partial pressure of eachmolecular contaminant (H₂O, H₂, O₂, Ar, CO₂, etc.) is monitored. Theoutgasing of the contaminants is accelerated through the baking so thatthe background of the RGA-QMS is reduced.

[0043] Sequentially, the contamination for the gas line is analyzed, inorder to analyze the integrity of each supply line (SiH₄, PH₃, and N2).N₂ gas at 500 SCCM is introduced into each supply line, one by one. Gasinside the process chamber is then sampled and analyzed to determine ifthe gas supply line is leaking.

[0044] Then, a specific process for semiconductor wafers is carried out,and sampling is carried out so as to analyze the process. At this time,for example, in a storage-polysilicon deposition step of DRAMprocessing, continuous sampling may be carried out in the prepurge andafter-purge step as well as in the deposition step. The manifold ismaintained below the 0.9 Torr, pressure of the process chamber, by wayof the critical orifice on the sampling manifold. of the RGA-QMS. FIG. 4shows a typical analysis trend for the storage-polysilicon formationprocess.

[0045] After the specific process for semiconductor wafers is completed,the boat containing the wafers is unloaded from a process chamber, andthe waste-gas therein is discharged. Then, a ClF₃ in-situ cleaningprocess is carried out. In the case of depositing storage-poly layer toa thickness of 48,000 Å, the adhered layer inside the process chamber isetched away using a mixture of 2800 SCCM N₂ gas and700 SCCM ClF₃ gas.

[0046] Then, cleaning process steps are analyzed to determine the EPD(End Point Detection) of cleaning process. The cleaning process isanalyzed by alternately varying the pressure and temperature of theprocess chamber while maintaining the flow of cleaning gas (for example,N₂ gas of 2800 SCCM, and ClF₃ gas of 700 SCCM). Like the storage-polyformation process analysis, the EPD analysis of the cleaning process isperformed throughout the whole cleaning process. FIG. 5 shows ananalysis trend for the in-situ cleaning process by ClF₃ afterstorage-poly deposition process. As shown in FIG. 5, the cleaningprocess is divided into 3 steps. The first step is evacuating andpurging the chamber prior to cleaning, as shown in FIG. 5, during theSCCM time from 0 to 50. The ClF₃ etching is carried out in the secondstep, and is represented in FIG. 5 from 50 to about 280 scan. The thirdstep is the evacuation and purging after the etching is complete, whichcorresponds to the time after 280 scan.

[0047] As shown in FIG. 5, the EPD of the cleaning process is the point100 around 280 scan. At about point 100 (scan=280), the concentration ofHF+ equals the concentration of SiF3+ in the process chamber. At thatpoint, the ClF₃-N₂ gas mixture has largely etched away thesilicon-containing layers on the inside walls of process chamber 10.After that point, continued flow of etchant gas into the process chamberresults in unwanted etching of the polysilicon layer by the fluoride andchloride radicals generated by ClF₃. The unwanted etching of thepolysilicon layer is indicated, according to the invention, by thedetection of HF. HF is a polysilicon etching byproduct that is notpresent in relatively high concentrations during the etching of siliconfrom the process chamber walls. By repeatedly carrying out the samestorage-poly deposition process by varying the pressure and temperatureof process chamber 10, the flow rate of the ClF₃, and determining EPDfor each case, the process time for each step of the cleaning processcan be optimized. The results of the optimization as above are shown inFIGS. 6, 7 and 8. FIG. 6 is a graph correlating etch rate in thecleaning process to the pressure inside a process chamber 10. FIG. 7 isa graph correlating the etch rate during the cleaning process to thetemperature inside process chamber 10. FIG. 8 is a graph correlatingetch rate in the cleaning process to ClF₃ flow rate inside a processchamber. The effectiveness of the cleaning can be evaluated bymonitoring the particles present in process chamber 10 before and afterthe cleaning process. Metal and ion contaminants such as Fe, Cr, Ni, Zn,Ti, S, Cl, F, NH₄ can also be monitored using with TXRF/HPIC (TotalX-ray Reflection Fluorescence/High Performance Ion Chromatography)before and after the cleaning process.

[0048] Therefore, according to the present invention, without removingthe process tubes, the process chamber can be in-situ cleaned so thatthe life of process chamber is increased, the cleaning time isshortened, and productivity is improved.

[0049] In addition, according to the present invention, the in-situcleaning process can be optimized so that the life of the processchamber is increased and cleaning time is shortened. Further, accordingto the present invention, the processes for the wafers continuously ismonitored, and analyzed so that the process malfunctioning is preventedcontributing to the increase of the productivity. Still further, whilethe present invention has been described in detail, it should beunderstood that various changes, substitutions and alterations can bemade hereto without departing from the spirit and scope of the inventionas defined by the appended claims.

What is claimed:
 1. A method of forming a semiconductor devicecomprising the steps of: providing a process chamber having an interiorsurface; providing a workpiece in the process chamber; forming a firstlayer of material on the workpiece; forming a second layer of materialon the interior surface of the process chamber; selectively etching insitu the second with a gas comprising ClF₃; monitoring the gascomposition within the process chamber; and monitoring the processchamber gas composition and thereby determining when the second layerhas been substantially depleted.
 2. The method of claim 1 wherein thestep of monitoring the process chamber gas composition includes thesteps of: monitoring a first layer etching by-product; monitoring asecond layer etching by-product; determining when the first layeretching by-product is at a predetermined concentration relative to thesecond layer etching by-product.
 3. The method of claim 2 wherein thefirst layer etching by-product is SiF3+ and the second layer etchingby-product is HF+.